/**
 * C program to reverse a Doubly linked list
 */

#include <stdio.h>
#include <stdlib.h>

/*
 * Basic structure of Node
 */
struct node
{
    int data;
    struct node *prev;
    struct node *next;
} *head, *last;

/*
 * Functions used in this program
 */
void createList(int n);
void displayList();
void reverseList();

int main()
{
    int n, data, choice = 1;

    head = NULL;
    last = NULL;

    /*
     * Runs forever until user chooses 0
     */
    while (choice != 0)
    {
        printf("============================================\n");
        printf("DOUBLY LINKED LIST PROGRAM\n");
        printf("============================================\n");
        printf("1. Create List\n");
        printf("2. Reverse List\n");
        printf("3. Display list\n");
        printf("0. Exit\n");
        printf("--------------------------------------------\n");
        printf("Enter your choice : ");

        scanf("%d", &choice);

        switch (choice)
        {
        case 1:
            printf("Enter the total number of nodes in list: ");
            scanf("%d", &n);
            createList(n);
            break;
        case 2:
            reverseList();
            break;
        case 3:
            displayList();
            break;
        case 0:
            break;
        default:
            printf("Error! Invalid choice. Please choose between 0-3");
        }

        printf("\n\n\n\n\n");
    }

    return 0;
}

/**
 * Creates a doubly linked list of n nodes.
 * @n Number of nodes to be created
 */
void createList(int n)
{
    int i, data;
    struct node *newNode;

    if (n >= 1)
    {
        /*
         * Create and link head node
         */
        head = (struct node *)malloc(sizeof(struct node));

        printf("Enter data of 1 node: ");
        scanf("%d", &data);

        head->data = data;
        head->prev = NULL;
        head->next = NULL;

        last = head;

        /*
         * Create and link rest of the n-1 nodes
         */
        for (i = 2; i <= n; i++)
        {
            newNode = (struct node *)malloc(sizeof(struct node));

            printf("Enter data of %d node: ", i);
            scanf("%d", &data);

            newNode->data = data;
            newNode->prev = last; // Link new node with the previous node
            newNode->next = NULL;

            last->next = newNode; // Link previous node with the new node
            last = newNode;       // Make new node as last/previous node
        }

        printf("\nDOUBLY LINKED LIST CREATED SUCCESSFULLY\n");
    }
}

/**
 * Display the content of the list from beginning to end
 */
void displayList()
{
    struct node *temp;
    int n = 1;

    if (head == NULL)
    {
        printf("List is empty.\n");
    }
    else
    {
        temp = head;
        printf("DATA IN THE LIST:\n");

        while (temp != NULL)
        {
            printf("DATA of %d node = %d\n", n, temp->data);

            n++;

            /* Move pointer to next node */
            temp = temp->next;
        }
    }
}

/**
 * Reverse order of the doubly linked list
 */
void reverseList()
{
    struct node *current, *temp;

    current = head;
    while (current != NULL)
    {
        /*
         * Swap the previous and next address fields of current node
         */
        temp = current->next;
        current->next = current->prev;
        current->prev = temp;

        /* Move the current pointer to next node which is stored in temp */
        current = temp;
    }

    /*
     * Swap the head and last pointers
     */
    temp = head;
    head = last;
    last = temp;

    printf("LIST REVERSED SUCCESSFULLY.\n");
}


Output

============================================
DOUBLY LINKED LIST PROGRAM
============================================
1. Create List
2. Reverse List
3. Display list
0. Exit
--------------------------------------------
Enter your choice : 1
Enter the total number of nodes in list: 4
Enter data of 1 node: 10
Enter data of 2 node: 20
Enter data of 3 node: 30
Enter data of 4 node: 40

DOUBLY LINKED LIST CREATED SUCCESSFULLY

============================================
DOUBLY LINKED LIST PROGRAM
============================================
1. Create List
2. Reverse List
3. Display list
0. Exit
--------------------------------------------
Enter your choice : 3
DATA IN THE LIST:
DATA of 1 node = 10
DATA of 2 node = 20
DATA of 3 node = 30
DATA of 4 node = 40

============================================
DOUBLY LINKED LIST PROGRAM
============================================
1. Create List
2. Reverse List
3. Display list
0. Exit
--------------------------------------------
Enter your choice : 2
LIST REVERSED SUCCESSFULLY.


============================================
DOUBLY LINKED LIST PROGRAM
============================================
1. Create List
2. Reverse List
3. Display list
0. Exit
--------------------------------------------
Enter your choice : 3
DATA IN THE LIST:
DATA of 1 node = 40
DATA of 2 node = 30
DATA of 3 node = 20
DATA of 4 node = 10

============================================
DOUBLY LINKED LIST PROGRAM
============================================
1. Create List
2. Reverse List
3. Display list
0. Exit
--------------------------------------------
Enter your choice : 0